Method and device for controlling the paper feed in a processor-driven printer

Abstract

The device embodying the invention is intended to equip a processor-driven printer comprising a hopper capable of containing and supporting a freely rotating roll of paper, a guide and drive means enabling the web of paper to be led from the roll to a drive device, to a line by line print station and then to an output orifice. It comprises at least one first detector capable of detecting marks affix on the web, in an area not used for printing. The invention applies to a printer of the type used in man/machine dialog or in remote transmission.

We claim: 
     
       1. A method for monitoring the paper feed in a processor-driven printer comprising a hopper capable of containing and supporting a freely rotating roll of a paper web, a guide and drive means enabling said paper web to be led on a path from the roll to a drive device, to a print station and then to an output orifice, said method comprising a succession of cycles each comprising the steps of: affixing a mark on said paper web by means of a marking device situated at a first location on said path, inside said printer,   detecting presence or absence of the mark at least at a second location on said path,   measuring in real-time a parameter representative of position of said mark throughout a portion of said path from the first location to the second location,   comparing said parameter with reference values defining a theoretical position of said second location, and   at the instant when said measured position corresponds with said theoretical position, verifying the presence of said mark, and sending a fault signal if said measured position does not correspond with said theoretical position.   
     
     
       2. The method as claimed in claim 1, wherein said parameter is measured by counting lines of writing and therefore feed steps of said paper web. 
     
     
       3. The method as claimed in claim 1, wherein said marks are affixed periodically on standard paper in one of lateral margins of said paper web not used for printing, each of said cycles further comprising the step of checking that said mark is absent at the instant the position measured is equal to said theoretical position less half a theoretical distance between two successive marks. 
     
     
       4. The method as claimed in claim 1, wherein said marks are affixed by said print station. 
     
     
       5. The method as claimed in claim 1, wherein said marks are affixed by an ancillary printing device independent to said print station and situated on said path, upstream of said print station. 
     
     
       6. The method as claimed in claim 1, wherein each of said cycles further comprises detecting presence or absence of paper on a part of said path situated upstream of printing means used for printing said mark. 
     
     
       7. A method for monitoring the paper feed in a processor-driven printer comprising a hopper capable of containing and supporting a freely rotating roll of a paper web, a guide and drive means enabling said paper web to be led on a path from the roll to a drive device, to a print station and then to an output orifice, said method comprising a succession of cycles each comprising the steps of: detecting presence or absence of a mark at several successive locations on said path between a first location and a last location,   measuring in real-time a parameter representative of position of said mark all along a portion of said path from said first location to said last location,   comparing said parameter with reference values defining respective theoretical positions of said successive locations, and   at instants when said measured position corresponds with one of said theoretical positions of a location, verifying that said mark is indeed detected at said location, and sending a fault signal if said mark is not detected at said location.   
     
     
       8. The method as claimed in claim 7, wherein each of said cycles further comprises, at each of said locations excepting said first location, detecting with a two-level threshold three distinct statuses: presence of unmarked paper, presence of marked paper, and absence of paper. 
     
     
       9. The method as claimed in claim 7, wherein said several successive locations are separated by distances which are integral multiples of the length of a mark. 
     
     
       10. A device for controlling paper feed in a processor-driven printer, said device comprising: a hopper capable of containing and supporting a freely rotating roll of a paper web,   a guide and drive means enabling said paper web to be led on a path from the roll to a drive device, to a line by line print station and then to an output orifice,   a marking device for affixing marks one by one on said paper web, situated at a first location on said path inside said printer,   at least one first detector for detecting presence or absence of marks affixed on said paper web at least at a second location on said path in an area not used for printing,   means for real-time measuring a parameter representative of position of a mark throughout a portion of said path from the first location to the second location,   means for comparing said parameter with reference values defining a theoretical position of said second location, and   means for verifying the presence of a mark at an instant when said measured position corresponds with said theoretical position, and means for sending a fault signal if no mark is detected at said instant.   
     
     
       11. The device as claimed in claim 10, wherein said first detector is located downstream of said print station. 
     
     
       12. The device as claimed in claim 10, further comprising an additional detector situated upstream of said print station, said additional detector being designed to detect presence or absence of paper. 
     
     
       13. The device as claimed in claim 10, wherein said first detector is capable of detecting three statuses: presence of unmarked paper,   presence of marked paper, and   absence of paper.